1. Field of the Invention
The present invention relates to a control apparatus for controlling an electric power steering mechanism.
2. Description of the Related Art
Two documents have been disclosed regarding an electric power steering mechanism. One is U.S. Pat. No. 5,720,361, and the other is U.S. Pat. No. 5,999,869. In these documents, an abnormality-detecting circuit for determining a failure of the electric power steering mechanism is disclosed.
According to the prior art, an abnormality detecting counter (hereinafter referred to as an abnormal counter) counts up each time an abnormality of the electric power steering mechanism is detected, and when the count value reaches a failure deciding value, a CPU decides that the power steering mechanism driven by an electric motor is in a state of a failure and the current supplied to the electric motor is stopped.
However, when the abnormal counter cannot detect an abnormality before it reaches the failure determining value, the CPU immediately decides that the electric power steering mechanism is normal and the abnormal counter is reset to zero.
The above-described prior art has the following problems.
According to the above-mentioned logic to detect a failure, a failure state can be determined as long as the detection of abnormality due to a failure continues. However, when the abnormality is in a driving circuit system for the electric power steering mechanism (such as a short circuit between a motor terminal and a battery line, a short circuit between the motor terminal and a ground line, a short circuit between motor terminals, or a failure of the motor current detecting circuit), the current, and thus the steering torque value, hunts due the presence of the control system or the steering system, so that the abnormality is not continuously detected even though the abnormality continues in the driving circuit system. In such a case, a failure of the electric power steering system cannot be surely determined.
Accordingly, an object of the present invention is to provide a control apparatus of an electric power steering mechanism, which can surely determine whether or not the power steering mechanism is in a failure state.
To attain the above object, according to a first aspect of the present invention, there is provided a control apparatus for controlling an electric power steering mechanism comprising:
a torque sensor mounted on a steering shaft for detecting a steering torque signal;
an indicating value calculating unit for calculating a motor current indicating value based on the steering toque signal detected by the torque sensor and a vehicle speed detected by a vehicle speed sensor;
an electric motor for providing a steering assist force to the steering shaft;
a motor current detecting unit for detecting a motor current flowing in the electric motor;
a motor drive circuit for driving the electric motor;
a drive signal calculating circuit for calculating a drive signal from a current deviation between the motor current indicating value and the motor current detected value, and transferring the drive signal to the motor drive circuit;
an abnormal detecting unit for detecting whether the electric power steering mechanism is abnormal or normal at each sampling time; and
a failure deciding unit for detecting failure of the electric power steering mechanism when an abnormal counter is incremented at every detection of abnormality detected by the abnormal detecting unit, and when the abnormality counter reaches a failure deciding value;
wherein, the failure deciding unit returns the count value of the abnormal counter from the held value to zero when the abnormal detecting unit sequentially detects normality during a predetermined number of sampling times, even if the abnormal detecting unit once detects abnormality.
According to the above construction, even when the driving circuit system in the electric power steering mechanism is in a failure state, the abnormal counter is not reset too early but is continuously incremented.
When the count value of the abnormality counter reaches a failure deciding value, the failure-deciding unit determines that the electric power steering mechanism is in a failure state.
In addition, even when the abnormal detecting unit once detects abnormality, the failure-deciding unit resets the abnormal counter to zero only after the abnormal detecting unit sequentially detects normality during a predetermined number of sampling times. As a result, an erroneous decision, of deciding too early that the electric power steering system is in a failure state, can be prevented.
As a result, according to the first aspect of the present invention, it can be surely determined whether or not the electric power steering mechanism is in a failure state.
According to a second aspect of the present invention, the abnormal detecting unit has a hysteresis characteristic in order to detect whether the electric power steering mechanism is abnormal or normal. The abnormal detecting unit detects, at each sampling time, whether the electric power steering mechanism is abnormal or normal. When the abnormal detecting unit detects an abnormal state, the abnormal counter is incremented.
After the abnormal detecting unit detects an abnormal state, when the abnormal detecting unit detects a normal state or an indefinite state, which is neither abnormal nor normal, the abnormal counter holds its count value.
By this second aspect of the present invention, even when the electric power steering mechanism is in a failure state or has a high possibility of failure, the abnormal counter is not reset too early but surely counts up even after the abnormal detecting unit detects a normal state or an indefinite state.
According to a third aspect of the present invention, the abnormal detecting unit detects whether the electric power steering mechanism is normal or abnormal, based on at least one of a detected value of the motor current, a detected value of the motor voltage, a detected value of the battery voltage, and the motor current indicating value.
By this third aspect, the abnormal detecting unit can detect, with high precision, whether the electric power steering mechanism is normal or abnormal.
According to a fourth aspect of the present invention, the abnormal detecting unit detects that the electric power steering mechanism is normal under conditions where the detected value of the motor current is included within a normal range, where the detected value of the motor voltage is included within a normal range, where the detected value of the battery voltage is included within a normal range, and where the motor current indicating value is included within a normal range.
The abnormal detecting unit detects that the electric power steering mechanism is abnormal under the condition where the detected value of the motor current is not included within the normal range, where the detected value of the motor voltage is not included within the normal range, where the detected value of the battery voltage is not included within the normal range, or where the motor current indicating value is not included within the normal range.
By this fourth aspect of the present invention, the abnormal detecting unit can detect, with a high precision, whether the electric power steering mechanism is normal or abnormal.
According to a fifth aspect of the present invention, the control apparatus for controlling the electric power steering mechanism includes means for setting, when the abnormal detecting unit sequentially detects normality after the abnormal detecting unit once detects abnormality, a time required for sampling times to return the count value, counted by the abnormal counter from a holding value to zero, to a period longer than a hunting period which occurs in a control system and a steering system.
By this fifth aspect, a failure of the electric power steering mechanism, which is the hunting of the steering shaft caused due to the presence of the control system and the steering system, can also be determined as a failure.